Electrified powertrain with integrated charger

ABSTRACT

A vehicle has an electric machine including two sets of galvanically isolated windings, first and second inverters each coupled with only one of the sets, and a traction battery. The vehicle also has a switching arrangement that, during charge, couples the first inverter with a port such that current from a remote source flows through one of the sets and induces a voltage in the other of the sets to charge the battery while isolating the source from the battery.

TECHNICAL FIELD

This disclosure relates to electric drive systems for automotive vehicles, and charging arrangements associated therewith.

BACKGROUND

Hybrid-electric vehicles (HEVs) and battery electric vehicles (BEVs) may rely on a traction battery to provide power to a traction motor for propulsion, and a power inverter therebetween to convert direct current (DC) power to alternating current (AC) power. The typical AC traction motor is a three-phase motor that may be powered by three sinusoidal signals each driven with 120 degrees phase separation. Also, many electrified vehicles may include a DC-DC converter to convert the voltage of the traction battery to an operational voltage level of the traction motor.

SUMMARY

A vehicle has an electric machine including two sets of galvanically isolated windings, first and second inverters each coupled with only one of the sets, a traction battery, and a switching arrangement. The switching arrangement couples the first inverter with a port such that current from a remote source flows through one of the sets and induces a voltage in the other of the sets to charge the battery while isolating the source from the battery.

A method for a vehicle power system includes coupling by a controller a first inverter with a charge port such that current from a remote source flows through the first inverter and a first set of windings of an electric machine and induces a voltage in a second set of windings of the electric machine that is galvanically isolated from the first set to charge a traction battery while isolating the battery from the source.

A vehicle has an electric machine including two sets of galvanically isolated windings, a traction battery, and a switching arrangement. The switching arrangement, during charge, couples one of the sets with a charge port such that current from a remote source flows through the one and induces a voltage in the other of the sets to charge the battery while isolating the source from the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a typical on-board automotive vehicle charger.

FIG. 2 is a schematic representation of a multi-phase electric machine.

FIG. 3 is a phasor diagram of a multi-phase electric machine.

FIGS. 4a and 4b are schematic representations of effective inductance of electric machines.

FIG. 5 is a block diagram of a vehicle with an integrated charger.

FIG. 6 is a schematic representation of an electric drive for a six-phase electric motor.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are described herein. However, the disclosed embodiments are merely exemplary and other embodiments may take various and alternative forms that are not explicitly illustrated or described. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.

The processes, methods, logic, or strategies disclosed may be deliverable to and/or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, logic, or strategies may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on various types of articles of manufacture that may include persistent non-writable storage media such as ROM devices, as well as information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, logic, or strategies may also be implemented in a software executable object. Alternatively, they may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.

Despite differences in their architectures, electric vehicles (EVs) have similarities in their structures. For instance, a battery, inverter, and electric motor are typically the main building blocks of any EV. To energize the battery and provide power for the motor, two types of chargers are employed: on-board chargers and off-board (stand-alone) chargers. On-board chargers give flexibility to charge anywhere there is an electric power outlet available. The on-board type has the potential drawback of adding weight, volume, and cost to the vehicles. Thus, any possibility of avoiding the issues of additional charger weight, space, and cost by using available hardware, mainly the electric motor and the inverter, to charger the battery is desirable. Considering the case in EVs, which during charging time the vehicle is not driven and during driving time it is not intended to charge the battery pack except for regeneration at braking, the integration of an on-board charger and traction system seems to be a feasible option.

There are specific requirements for on-board chargers (including galvanic isolation) which need to be fulfilled for any integrated system. Other aspects to consider regarding integrated chargers are voltage level adaption, unwanted developed torque in the motor during charging, efficiency, low harmonic contents in the current from the grid, and possible mandatory unity power factor operation.

Due to many advantages that integrated chargers can introduce to the system, different types of integrated chargers have been previously reported. Most of these integrated chargers however suffered from the lack of galvanic isolation in their structure. Here, certain proposed integrated charges provide galvanic isolation for the charging process.

Currently, some manufactures do not use integrated chargers and instead focus on on-board chargers which do not utilize the electric drive components. FIG. 1 illustrates a vehicle 10 with an on-board charger arrangement 12 operatively arranged with a power source 14. The on-board charger arrangement 12 includes a charging port 16, an electro-magnetic interference (EMI) filter 18, a diode bridge 20, a DC/AC converter 22, a transformer 24, an AC/DC filter 26, a boost converter 28, and a traction battery 30. The EMI filter 18 reduces high frequency electronic noise before providing input to the diode bridge 20. The transformer 24 provides isolation between the DC/AC converter 22 and the AC/DC converter 26. The boost converter 28 performs power factor correction (and possible voltage adjustment) to output from the AC/DC converter 26 before providing input to traction battery 30.

For high power applications (e.g., electric vehicles), large AC machines sometimes include multiple windings (FIG. 2) fed by multiple inverters. Here, a1 is the inductance of phase a of winding set 1, a2 is the inductance of phase a of winding set 2, b1 is the inductance of phase b of winding set 1, b2 is the inductance of phase b of winding set 2, c1 is the inductance of phase c of winding set 1, c2 is the inductance of phase c of winding set 2, d1 is the inductance of winding set 1 along the d-axis, d2 is the inductance of winding set 2 along the d-axis, q1 is the inductance of winding set 1 along the q-axis, q2 is the inductance of winding set 2 along the q-axis, and ω is the electrical speed. The rotor d-axis is at the angle θ₁ relative to the axis of phase a₁, and at θ₂ relative to the axis of phase a₂, and α=θ₂−θ₁.

Due to the structure of these multiphase machines, the mutual inductance (magnetic coupling) among groups of phases, in addition to individual phases, is inevitable. This is of interest not only for determining performance and designing control systems, but also for analyzing fault tolerance. This cross coupling among the windings (phases) can form a transformer when the energy is injected to only one group of windings.

Under AC steady-state conditions, the RMS values of the d- and q-axis flux-linkages Ψ_(d) and Ψ_(q) can be combined into a phasor: Ψ_(i)=Ψ_(di) +jΨ _(qi)  (1) I _(i) =I _(di) +jI _(qi)  (2) V _(i) =V _(di) +jV _(qi) =R _(i) I _(i) +jωΨ _(i)  (3) where, i=1, 2 and V_(di)=R_(i) I_(di)−X_(qi) I_(qi)−X_(q1q2)I_(q2) and V_(qi)=E_(qi)+R_(i)I_(qi)+X_(di)I_(di)+X_(d1d2)I_(d2). These equations have been described graphically in FIG. 3, where Ψ_(di) is the flux linkage of winding set i along the d-axis, Ψ_(qi) is the flux linkage of winding set i along the q-axis, Ψ_(i) is the total flux linkage of winding set i, I_(di) is the current of winding set i along the d-axis, I_(qi) is the current of winding set i along the q-axis, I_(i) is the total current of winding set i, V_(di) is the voltage applied to winding set i along the d-axis, V_(qi) is the voltage applied to winding set i along the q-axis, V_(i) is the total voltage applied to winding set i, Ri is the resistance of winding set i, ω is the electrical speed, E_(q1) is the back electromotive force (EMF) along the q-axis seen by winding set 1, X_(d1) is the reactance of winding set 1 along the d-axis, X_(q1) is the reactance of winding set 1 along the q-axis, X_(d1d2) is the mutual reactance of winding sets 1 and 2 along the d-axis, X_(q1q2) is the mutual reactance of winding sets 1 and 2 along the q-axis, ϕ is the angle between I₁ and V₁, γ is the angle between I₁ and E_(q1), and δ is the angle between V_(q1) and E_(q1).

The cross-coupling terms appear in the phasor diagram as additional voltage-drops, which tend to limit the current. If α=0 (angle between group of phases), there is tightly coupled inductances between the two sets, as already observed; and if these sets are fed from a common voltage source, the current in each set will be approximately half the current that would flow in one set if the other were open-circuited. This is a practical point because it implies that in a duplex winding, if one set is open-circuited the current in the other set could increase by a factor approaching 200%, if it were not regulated. Likewise if one set is short-circuited, the impedance of the second set will be reduced and its current could also increase to a high value if it is not regulated.

The behavior of the duplex sets is analogous to that of parallel inductances, see FIGS. 4a and 4b , with an equivalent inductance of

$\begin{matrix} \frac{{L_{1}L_{2}} - M^{2}}{L_{1} + L_{2} - {2M}} & (4) \end{matrix}$ In this case if L1=L2=L, then the effective inductance becomes

$\begin{matrix} \frac{L + M}{2} & (5) \end{matrix}$ where Ψ₁ is the flux of coil 1, Ψ₂ is the flux of coil 2, M is the mutual inductance of the coils, L₁ is the inductance of coil 1, L₂ is the inductance of coil 2, and i is the total current. Furthermore, when α=0, M becomes close to L and the effective equivalent inductance becomes L. At the same time, the coupling coefficient between the phases will be k=1 (theoretically). The total current is that which is limited by L, and half the current flows in each set. But if one set is open-circuited, the same total current will tend to flow in one set. The implication is that regulation of the current may be helpful.

Since the traction system and on-board charger are not functional simultaneously, and considering the acceptable amount of coupling between the phases, as discussed above, employing a multiphase electric machine as a transformer to create isolation for an on-board charger seems to be a logical approach. FIG. 5 illustrates a high-level proposed architecture for an integrated onboard charger and traction system. In this example, vehicle 32 includes a transmission 33 and differential 34 arranged to directly drive wheel/tire assemblies 36. (Wheel/tire assemblies 37 follow the driven wheel/tire assemblies 36.) The vehicle 32 also includes an electric drive system 38 configured to be selectively coupled with the transmission 33 via a clutch 40. The electric drive system 38 includes an electric motor 42, an inverter and windings switching device 44, and a traction battery 46. The inverter and windings switching device 44 is arranged to receive power from an external charge cord 48. Power received from the external charge cord 48 can be provided to the traction battery 46 via the inverter and windings switching device 44 for charging purposes. Similarly, power received from the traction battery 46 can be provided to the electric motor 42 via the inverter and windings switching device 44 to operate the electric motor 42. A controller 49 (or controllers, used interchangeably herein) is in communication with and controls the electric drive system 38. Of course, other and/or different vehicle configurations are contemplated. Such configurations, for example, need not include the transmission 33, or clutch 40, etc.

As explained in further detail below, the inverter and windings switching device 44 and electric motor 42 perform as the traction system during vehicle propulsion, and participate in the charging process during charging of the traction battery 46.

FIG. 6 shows one proposed topology for the electric drive system 38 of FIG. 5. In this example, the electric motor 42 includes two sets of windings 52, 54, and the inverter and windings switching device 44 includes a pair of inverters 56, 58 and switches S1, S2. The vehicle 32 also includes a power factor correction stage 61, diode bridge rectification stage 62, EMI filter 63, and charge port 64. The charge port 64 is shown coupled with a remote power source 66.

In traction mode, the controller 49 (FIG. 5) connects the switches S1, S2 to position 1 between the traction battery 46 and the inverter 56 thereby isolating the inverter 56 from the charge port 64. The traction battery 46 is thus connected to both the inverters 56, 58. Each of the inverters 56, 58 can provide half the required power to the windings 52, 54 respectively, and the controller 49 can synchronize control and power flow. (In traction mode, the charging port 64 would of course not be connected with the remote power source 66.)

In charging mode, the controller 49 (FIG. 5) connects the switches S1, S2 to position 2 between the inverter 56 and the power factor correction stage 61. The DC link capacitor of the inverter 56 is charged through the power factor correction stage 61, and the inverter 56 converts this DC power to AC power (with required frequency). The AC power flows through the windings 52, which induces a voltage at and a corresponding current flow through the windings 54. The inverter 58 then rectifies this current before it is injected into the traction battery 46. Thus, in both traction mode and charging mode, the charge port 64 is completely isolated from the traction battery 46.

Considering the level of power transferred through the windings 52, 54 and core (e.g., ˜8 kW), core saturation is not likely. Also to achieve a zero voltage source, a three-phase inductor can be added in series with the windings 52 if the leakage inductance of the electric machine 42 is not high enough for this purpose. Additionally, if the coupling coefficient is not high enough, a set of inductors and capacitors (resonant tank) can be added in series with the windings 52.

During the charging process, maximum coupling and consequently maximum mutual inductance is desirable. The controller 49 can place the rotor (in the case of permanent magnet motors) of the electric machine 42 in a position that provides the maximum coupling coefficient between phases. Having a resolver in place may simplify this task. Known testing or simulation techniques, for example, can be used to identify the rotor position that maximizes the coupling coefficient. This position can then be stored within memory accessible by the controller 49 (or obtained online during operation) such that prior to charge, the controller 49 can identify current rotor position via the resolver, and then cause the rotor to move to the desired position to maximize coupling. Other techniques may also be used.

Some embodiments may offer certain advantages. The DC-DC stage of an on-board charger can be eliminated. The power level can be higher than an equivalent level 1 or level 2 charger. Maximum power capability depends on the motor structure and core saturation limit. The proposed integrated charger can be bidirectional to transfer power between grid and battery. The proposed converter can be employed for single-phase, two-phase, or three-phase input from the utility grid by changing the design of the power factor correction stage, diode bridge rectification stage, and EMI filter.

The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications. 

What is claimed is:
 1. A vehicle comprising: an electric machine including two sets of galvanically isolated windings; first and second inverters each coupled with only one of the sets; a traction battery; a switching arrangement configured to couple the first inverter with a port such that current from a remote source flows through one of the sets and induces a voltage in the other of the sets to charge the battery while isolating the source from the battery, wherein the second inverter is configured to rectify the voltage; and a controller configured to, prior to charging the traction battery, move a rotor of the electric machine to a target position.
 2. The vehicle of claim 1, wherein the switching arrangement is further configured to, during propulsion, couple the first inverter with the traction battery while isolating the port from the first inverter.
 3. The vehicle of claim 1, wherein the electric machine is a six-phase electric machine.
 4. A method for a vehicle power system comprising: coupling by a controller a first inverter with a charge port such that current from a remote source flows through the first inverter and a first set of windings of an electric machine and induces a voltage in a second set of windings of the electric machine that is galvanically isolated from the first set to charge a traction battery while isolating the battery from the source; and responsive to propulsion mode, coupling by the controller the first inverter with the traction battery while isolating the charge port from the first inverter.
 5. The method of claim 4 further comprising rectifying by a second inverter the voltage.
 6. The method of claim 4 further comprising, prior to charging the traction battery, moving a rotor of the electric machine to a target position.
 7. A vehicle comprising: an electric machine including two sets of galvanically isolated windings; a traction battery; a switching arrangement configured to, during charge, couple one of the sets with a charge port such that current from a remote source flows through the one and induces a voltage in the other of the sets to charge the battery while isolating the source from the battery, and during propulsion, couple the first inverter with the traction battery while isolating the port from the first inverter; and a first inverter coupled with the one of the sets and a second inverter coupled with the other of the sets.
 8. The vehicle of claim 7, wherein the second inverter is configured to rectify the voltage.
 9. The vehicle of claim 8 further comprising a controller configured to, prior to charging the traction battery, move a rotor of the electric machine to a target position.
 10. The vehicle of claim 7, wherein the electric machine is a six-phase electric machine. 